1. Field of the Invention
The present invention relates to a method and a related electronic device for adjustment of a radio-frequency circuit by impedance loading features, more particularly, to a method and a related electronic device for reducing the amount of time and resources needed for designing the radio-frequency circuit.
2. Description of the Prior Art
The transmitting and receiving abilities of the radio frequency in the wireless communication device determine the communication quality of the wireless communication system. If the transmit signal power of the wireless communication device does not work well, it will affect the signal receiving quality of the base station; on the contrary, if the receiving sensitivity of the wireless communication device does not work well, it will affect the receiving efficiency of the wireless communication. In other words, once a problem appears in one of the Uplink and the Downlink, it will greatly influence overall communication quality, even lead to a communication disconnection. Therefore, the transmitting and receiving abilities of the radio-frequency circuit are considered when designing wireless communication devices in order to achieve the communication quality required.
Please refer to FIG. 1. FIG. 1 is a diagram illustrating a radio-frequency circuit 10, which is conventionally used on a wireless communication device. Radio-frequency circuit 10 comprises a radio-frequency transmitting module 12, a radio-frequency receiving module 14, an antenna switching module 16, an antenna 18, and an antenna matching circuit 20. Radio-frequency transmitting module 12 comprises a power amplifier 120 and a matching circuit 122 to enhance the signal power outputted from a radio-frequency signal processing unit for transmitting the signal into the air through antenna 18. Radio-frequency receiving module 14 comprises a low noise amplifier 140, a matching circuit 144, and a surface acoustic wave filter (SAW filter) 146 to receive wireless signal through antenna 18, and to transmit the received signal to the radio-frequency signal processing unit for demodulating or decoding, etc. Generally, a test point TP is used as boundary while designing radio-frequency circuit 10. First, the test point TP is connected to a test device, the characteristics of radio-frequency transmitting module 12 and radio-frequency receiving module 14 are adjusted under the condition that impedance is 50Ω to fit in with the design specification. Next, antenna 18 that is installed in radio-frequency circuit 10 is measured from test point TP by a network analyzer for adjustment of the shape of antenna 18 and the characteristics of antenna matching circuit 20 to attain the optimal standing wave ratio or reflection coefficient.
After the design of radio-frequency circuit 10 is completed, a wireless communication device installed with radio-frequency circuit 10 is placed in the three-dimensional microwave anechoic chamber for testing total radiation power (TRP) and total isotropic sensitivity (TIS), as shown in FIG. 2. TRP and TIS are used to evaluate the transmitting and receiving abilities of the wireless communication device, correlative illustration is described as follows.
TRP is the average value of outwardly radiated power of transmitter in the wireless communication device in omni directional space; it is to overall estimate the transmitting ability of a transmitter in the wireless communication device in three-dimensional space. The testing method of TRP is: set up the wireless communication device to the three-dimensional microwave anechoic chamber as shown in FIG. 2, estimate the effective isotropic radiated power (EIRP) respectively at each 15 degree interval between the θ-axis and φ-axis on a spherical coordinate system by controlling the location of the wireless communication device, and by carrying out the integral operation on all estimated results, TRP therefore can be obtained.
On the other hand, TIS is the receiving sensitivity of the receiver in the wireless communication device in omni directional space; it is to overall estimate the receiving ability of transmitter in the wireless communication device. The testing method of TIS is: estimate the effective isotropic sensitivity (EIS) respectively at each 30 degree interval between the θ-axis and φ-axis on a spherical coordinate system by controlling the location of the wireless communication device, and by carrying out the integral operation on all estimated results, TIS therefore can be obtained.
Thus after the design of the radio-frequency circuit 10 (not shown in FIG. 1 ) is completed, the TRP and the TIS of the wireless communication device are estimated in the three-dimensional microwave anechoic chamber to evaluate the transmitting and receiving abilities of the wireless communication device. After that, the designers may re-adjust the radio-frequency circuit 10 (not shown in FIG. 1) according to the estimated TRP and TIS in order to obtain the highest TRP and the lowest TIS conforming to the communication specification. Such designing process, however, takes too much time and resources; and the optimal TRP and TIS may not be obtained with limited time and resource.
As described above, a designer of the wireless communication device usually assumes the impedance of all frequency bands is 50Ω. In fact, in order to reduce the size of antenna and to conform to the requirements of multi-frequency bands, it is difficult for the impedance of antenna with a matching circuit to approach 50Ω; therefore designing becomes more difficult. Referring to FIGS. 3 to 6, for example, FIGS. 3 and 4 are diagrams illustrating the Smith Chart and the voltage standing wave ratio (VSWR) of a GSM triple-band antenna; FIGS. 5 and 6 are diagrams illustrating the Smith Chart and the VSWR of another GSM triple-band antenna. A corresponding communication system to the triple band as described above is: EGSM900 system, in which the receiving frequency band is between 925.2 MHz and 959.8 MHz and the transmitting frequency band is between 880.2 MHz and 914.8 MHz; DCS1800 system, in which the receiving frequency band is between 1805.2 MHz and 1879.8 MHz and the transmitting frequency band is between 1710.2 MHz and 1784.8 MHz; PCS1900 system, in which the receiving frequency band is between 1930 MHz and 1990 MHz and the transmitting frequency band is between 1850 MHz and 1910 MHz.
In FIGS. 3 and 5, it is difficult for all three frequency bands of the GSM triple-band antenna to meet the requirement of approaching 50Ω of impedance, this is why the designers are incapable of knowing with which antenna and its matching circuit the active radiation feature of the wireless communication device is able to perform best.